Flight Details
On 3 June 2007, a Boeing B737-800, registration EI-DPB, operated by Ryanair Ltd. as flight RYR586A, was on a scheduled IFR flight from London Stansted (EGSS) to Pisa Galileo Galilei (LIRP). The same day, a Cessna 560 Citation V Ultra, registration HB-VNW, operated by Swiss Eagle AG as flight EAB627, was on a commercial IFR flight from Toulon-Hyères (LFTH) to Zurich (LSZH). The serious incident occurred approximately 25 NM north-northwest of the SRN DVOR beacon.
Incident Sequence
RYR586A was cruising at FL370 and received clearance to descend to FL290, with the requirement to reach FL290 by waypoint ODINA. At 15:47:49 UTC, while at FL347 and descending, the flight was instructed to contact Milan (Sector EAN). Meanwhile, EAB627 was at FL300, approximately 30 NM south-southwest of waypoint CANNE, and had been coordinated to enter Zurich airspace at that altitude. At 15:48:47 UTC, EAB627 contacted Zurich Sector M2.
At 15:48:05 UTC, RYR586A established contact with Milan Sector EAN. The Milan controller issued a clearance at 15:48:54 UTC for a left turn direct to the PAR VOR, despite RYR586A still being in Zurich airspace. This turn placed RYR586A on a reciprocal course to EAB627. At the time, RYR586A was at FL320 with a reduced descent rate. EAB627 remained at FL300.
ATC Coordination
The short-term conflict alert (STCA) activated at Sector M2 at 15:49:46 UTC. The radar executive at Zurich (RE-M2) noticed the conflict and attempted to call the Milan controller but the call was not understood. The Milan controller stated that he expected RYR586A to continue its descent to FL290 and later instructed the flight to "expedite leaving 300" after becoming aware of the conflict. Both Milan controllers believed that increasing the descent rate would resolve the situation. However, they had expected RYR586A to be handed off to them only after the conflict was resolved by Zurich ATC.
TCAS and Crew Response
At 15:50:32 UTC, the Zurich RE-M2 informed EAB627 of traffic at 11 o'clock, same altitude, descending through their level. The EAB627 crew acknowledged a TCAS contact and reported looking out. They later stated they had a TCAS traffic advisory (TA), not a resolution advisory (RA). The B737 crew reported no TCAS alerts. The investigation revealed that the EAB627 crew initially incorrectly reported an RA over the radio but later corrected to a TA. The crew lacked precise knowledge of TCAS procedures.
Separation
The aircraft crossed paths with a minimum vertical separation of 650 ft and a lateral distance of 2.3 NM, nearly head-on. No resolution advisories were issued by either aircraft's TCAS. The incident occurred in Milan ATC airspace.